linux-kernel - Re: [RFC v2] iio: input-bridge: optionally bridge iio acceleometers to create a /dev/input interface

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Message-Id: <4C600F37-33E3-4C3D-B7D1-BBB85D5A2195@goldelico.com>
Date:   Fri, 10 May 2019 12:06:03 +0200
From:   "H. Nikolaus Schaller" <hns@...delico.com>
To:     Bastien Nocera <hadess@...ess.net>
Cc:     Jonathan Cameron <jic23@...nel.org>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Eric Piel <eric.piel@...mplin-utc.net>,
        linux-input@...r.kernel.org, letux-kernel@...nphoenux.org,
        kernel@...a-handheld.com, Hartmut Knaack <knaack.h@....de>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        linux-kernel@...r.kernel.org, linux-iio@...r.kernel.org
Subject: Re: [RFC v2] iio: input-bridge: optionally bridge iio acceleometers to create a /dev/input interface


> Am 10.05.2019 um 11:35 schrieb Bastien Nocera <hadess@...ess.net>:
> 
> On Fri, 2019-05-10 at 11:33 +0200, H. Nikolaus Schaller wrote:
>>> 
> <snip>
>> It does through "Input device name:" starting with "iio-bridge:" as
>> you can see in the commit message of [RFC v3]:
> 
> This makes it ABI, right?

The "Input device name:" is already ABI of the input system (although I guess the string is
built into the evtest tool). I think there are also /sys nodes which carry the same information.

But yes, if someone changes the "iio-bridge:" prefix in kernel code it breaks a user space lib
making use of it:

+	poll_dev->input->name = kasprintf(GFP_KERNEL, "iio-bridge: %s",
+						    indio_dev->name);
+	poll_dev->input->phys = kasprintf(GFP_KERNEL, "iio:device%d",
+						    indio_dev->id);

This type of exporting names seems to be quite common. E.g. "mmcblk0p1" which may end up
in some /etc/fstab.

> 
> Big fat warnings around the code that declares it would be appreciated.

Ok.